Nonaqueous electrolyte secondary battery

A positive electrode active material is composed of a sodium-containing oxide. The sodium-containing oxide contains NaALiBMO2+-alpha belonging to a hexagonal space group P63/mmc. In the NaALiBMO2+-alpha, M includes at least one of manganese (Mn) and cobalt (Co), the composition ratio A of sodium (Na) is not less than 0.5 but not more than 1.1, the composition ratio B of lithium (Li) is more than 0 but not more than 0.3, and a is not less than 0 but not more than 0.3.